Field of the Invention
The invention relates to a control configuration for tripping a restraint device in a motor vehicle in the case of a side-impact collision, including a sensor device having two acceleration sensors and supplying one longitudinal acceleration signal for accelerations parallel to a longitudinal axis of the vehicle and one transverse acceleration signal for accelerations transverse to the longitudinal axis of the vehicle, and a tripping circuit supplying an output signal determined by the longitudinal acceleration signal and the transverse acceleration signal, for tripping the restraint device if a limit value is exceeded by the output signal.
Control configurations for tripping a restraint device in a front-impact or oblique-impact collision are well known and are installed in motor vehicles on a mass-production basis. An acceleration sensor which is sensitive in the direction of the longitudinal axis of the vehicle detects a negative vehicle acceleration that is caused by a front-impact or oblique-impact collision. A tripping circuit processes the acceleration signal in accordance with an algorithm, which in the simplest case compares the amplitude of the acceleration signal with a limit value, and optionally trips a restraint device, such as driver and passenger-side air bags or belt tighteners. Due to the great distance between the site of impact and the passenger compartment, and because of the energy-absorbing effect of the crumple zone of the vehicle, a relatively long time can elapse before the tripping of the restraint device is permitted by the control configuration without impairing the protection that the restraint device provides to the passengers. That time is utilized to evaluate the acceleration signal. In that process, information is obtained about the severity and type of impact, especially by evaluating the late phases of the acceleration signal, in which the acceleration signal also reaches its maximum amplitude.
In a side-impact collision only a very short time span of a few milliseconds elapses before the control configuration must make the decision whether or not to trip the restraint device, because the distance between the impact site and the passenger compartment is so slight, and an only moderately energy-absorbing crumple zone develops. Within that time span, an acceleration signal which is transverse to the longitudinal axis of the vehicle and is elicited by a side-impact collision, is in its rising phase. The acceleration signal does not reach its maximum amplitude until a later phase. However, the tripping decision must already be made by that time, if the passengers are still to be protected effectively. Until now, acceleration sensors for detecting transverse accelerations have therefore been disposed in the doors, so that the weak acceleration signal can be picked up, near a possible site of a side-impact collision, while still in its first phase, the phase that is decisive for the tripping decision. An acceleration sensor disposed in the central region of the vehicle for picking up transverse accelerations picks up what at least in its first phase is an excessively weak acceleration signal, be cause of the damping by the vehicle body, and it must then derive a reliable tripping decision from that weak signal. If in the case of a weak acceleration signal, the limit value is necessarily set quite low as a tripping threshold value, then even slight fluctuations in an acceleration signal, or interference signals, can cause undesired tripping. That is why, until now, it appeared impossible for acceleration sensors and a tripping circuit for tripping the restraint device in the event of a side-impact collision to be disposed in a central control unit.
A front-impact or oblique-impact collision is another problem in previously known control configurations for tripping a restraint device in a side-impact collision: Each front-impact or oblique-impact collision also causes an acceleration transverse to the longitudinal axis of the vehicle, which can have a high amplitude especially in the late phases of the front-impact or oblique-impact collision. A transverse acceleration of that kind can lead to tripping of a restraint device intended to provide protection against a side-impact collision. In a side-impact collision involving that transverse acceleration, tripping would be desired, but that is not so in the case of a front-impact or oblique-impact collision.
A control configuration which is known from an article entitled "New Sensor Concepts for Reliable Detection of Side-Impact Collisions", in the Proceedings of the 14th International Technical Conference on Enhanced Safety of Vehicles, pages 1035-1038, has an air pressure sensor located in the vehicle door, that detects a rise in air pressure which occurs in the vehicle door in the event of a side-impact collision as a measure of the acceleration of the vehicle as a consequence of a side-impact collision. The air pressure sensors are connected to a tripping circuit, disposed in the central region of the vehicle, that trips a restraint device, such as side air bags, if the side-impact collision is sufficiently severe.
That kind of control configuration with decentralized sensors, with lines between the tripping circuit and the sensors and with plug connectors, has components which are intensive in terms of material consumption and the testing of which for operability requires considerable effort. Moreover, such a control configuration is expensive to manufacture, assemble, replace and repair.
A control configuration as defined at the outset above is known from German Published, Non-Prosecuted Patent Application DE 42 22 595 A1, corresponding to U.S. Pat. No. 5,202,831. That control configuration has two acceleration sensors, secured to the vehicle and disposed at an angle of 90.degree. from one another, so that the sensor device furnishes one longitudinal acceleration signal for accelerations parallel to the longitudinal axis of the vehicle and one transverse acceleration signal for accelerations transverse to the longitudinal axis of the vehicle. An acceleration vector is calculated from those two acceleration signals, in a tripping circuit. The vector is determined by its magnitude and its angle relative to the longitudinal axis of the vehicle. A restraint device, such as a side air bag, is selected from among a plurality of restraint devices disposed in the vehicle and is tripped, as a function of the acceleration vector.
A control configuration for tripping a restraint device in a vehicle in the event of a front-impact collision is known from an article entitled "Point to Point" by Norman Martin, in "Automotive Industries", July 1993, pages 49-51. To that end, two acceleration sensors at an angle of .+-.45.degree. from the longitudinal axis of the vehicle are disposed together with a tripping circuit in a common control unit. The restraint device is tripped as a function of the acceleration signals.
A control configuration for tripping a restraint device in a vehicle in a front-impact or oblique-impact collision is known from International Patent Publication WO 89/11986. The control configuration has a sensor device with two acceleration sensors offset by 90.degree. from one another. The sensor device furnishes one longitudinal acceleration signal for accelerations parallel to the longitudinal axis of the vehicle and one transverse acceleration signal for accelerations transverse to the longitudinal axis of the vehicle. The acceleration signals are evaluated both in an analog circuit and in a microprocessor, and they trigger the restraint device as soon as a front-impact or oblique-impact collision is detected as such.